In pathological diagnosis, first, taken tissue is dehydrated to be fixed, and blocking with paraffin is performed. Then, the tissue is cut into thin pieces each having a thickness of 2 to 8 μm, deparaffinization is performed, and the thin pieces are stained to be observed under a microscope. A pathologist makes, in this microscopic image, diagnosis based on morphologic information, such as change in size and shape of cell nuclei and change in pattern as tissue, and staining information. For example, in Patent Document 1, in a microscopic image, morphologic feature values such as area, density and so forth of each cell nucleus and degree of cell malignancy are calculated, and these morphologic feature values and degree of cell malignancy are observable as a cell image on a monitor.
As the tissue staining method usable in pathological diagnosis, there are known conventional dye staining methods (e.g. hematoxylin-eosin staining; hereinafter called “HE staining”) and dye staining methods using enzymes (e.g. DAB (diaminobenzidine) staining).
In pathological diagnosis, specifying a protein overexpressed in a tissue section and the amount of expression thereof can be very important information for prognosis prediction and determination of the feature treatment plan.
For example, HER2 protein, which codes HER2 gene, is a receptor glycoprotein which penetrates cell membranes, is composed of 3 domains which are extracellular, transmembrane and intracellular domains, and is said to be activated by phosphorylation of tyrosine residues when bonded with a growth factor and involved in growth and malignant transformation of cells through signaling pathways. Overexpression of HER2 protein can be seen in breast cancer, lung cancer, colon cancer, stomach cancer, bladder cancer and so forth.
Patent Document 2 describes a system which extracts cell nuclei from an image of biological tissue stained with DAB, identifies cell membranes in the image of the biological tissue based on the cell nuclei, determines a status of staining of the cell membranes, and evaluates expression of HER2 protein based on the determination result.
These days, a status of expression of a specific protein can be determined as follows: acquire a cell shape image showing shapes of cells in a tissue section and a fluorescence image showing expression of the specific protein as fluorescent bright points in a region the same as a region in the tissue section; estimate, from the cell shape image, cell regions each containing a region where the specific protein is expressed; extract the fluorescent bright points from the fluorescence image; calculate, based on cell nuclei and fluorescent bright points in each of the estimated cell regions, a feature amount of the cell region; and determine, based on the calculated feature amount, whether the cell region is cancer or not and the status of expression of the specific protein. (Refer to Patent Document 3.)